This term indicates the mountains "bought" or "sold" to other farms. 
We agree because it is in our mutual interest to see how the genes of our jewels can be combined, and we trust   in a high quality of puppies with mutual satisfaction.
In the same way, a breeder who is just starting out or who wants to mate a female, but in his breeding the males present are relatives or at rest, can ask other breeders for an agreement for a mating with their stallion.
There may be interests of a purely economic nature, in fact there is a monetizable "breeding right", or breeding interests: I want to introduce in the breeding a color that I do not have, a stronger physical characteristic, a prestigious name, or the like.
Whatever the interests, logistical, contractual and health problems must be faced.
Sanitary, because mating is a way of transmitting some diseases, as well as sharing the litter or bowls for the time necessary for mating. I refer mainly to FIV, FELV, Giardia and mushrooms, although I know that there are others that are more fearful but much rarer.
In general, a cat that enters another kennel is a source of danger because it brings with it something that others are not used to dealing with. The converse is also true, even for the newcomer there is some potential risk that awaits him. If our cats have overall good health and a good immune system, that is, they are used to going out, these dangers are completely negligible. 
Others, on the other hand, must be given a lot of attention. The advice is to agree between owners sufficiently in advance on the cats to be put together so as to be able to do two "snap tests" at a distance of one, or rather two, months from each other, for FIV and FELV antibodies. In practice, they are tests that are done with a drop of blood in a veterinary clinic, using a stick such as those used as a pregnancy test for humans: the pink comparison stripe and alongside a bar that can be colored or not. They have a high reliability and two big ones though:
1 - to avoid "false negatives" they are hypersensitive and consequently "false positives" are not rare: do not panic and immediately order a PCR (Polymerase Chain Reaction, your veterinarian knows what and how to do), a very more precise.
2 - there is the so-called "window period": from the moment of infection to the moment in which these tests detect the presence of antibodies, one or two months can pass. I know, if you do not know each other well and do not have the same starting information, it is a pain to explain why it is important to follow this procedure and do two tests. The risk is relatively low, but these are assessments that I make from my world, in which breeders do not have cats that frequent animals in partial or total freedom, I do not know of situations different from mine. I think everyone should inform and decide for themselves.
Last health advice: those who host the cat of others should do a sample coprological examination from the litter boxes at home and one of the cat's feces to mate. Here too there are two reasons: one, if there are intestinal parasites, it is absolutely necessary to intervene and a collective control on the farm at regular intervals is always a must. Second reason, if the guest ever complains of "unwanted presences" upon returning home, you will have the certificate that exonerates you. It seems excessive but the quarrel between breeders is not a rarity. In the same way, those who bring the cat to someone else's farm must have with them the two certificates of the negative FIV-FELV tests and that of the coprological examination that certifies the absence of intestinal parasites (Giardia in particular).
I am not of the opinion to also do the Coronavirus test,  Parvo or Calici Virus,  because if you have these doubts about the breeder in front of you it is better that you leave everything alone.  There is no immunologist who can make you rest assured if  Not  you have a strong awareness of what can be invisible and in every farm and even in your home.
For the HCM discourse there are two schools of thought among the owners of N / N: who is in favor of mating with N / P and who is unfavorable.
Personally I am in favor, that is, I do not choose the cat only on that parameter. My cats are almost all N / N so if I ever had to consider a mating with a N / P I would go to evaluate many other factors and not just that. I would certainly inquire about the parents of the cat in question, if they are still alive, same thing for the grandparents and it would be important that these cats are still on the farm and monitored annually. To exclude them entirely from any reproductive plan would be a great loss of genetic heritage and I do not see sufficient reasons for this. Obviously there is no mention of pairing two N / P, just as P / P must definitely be sterilized.
The contract
How does the essay say? Clear agreements long friendship! My advice is to put in black and white as much as possible, the obligations of the host and who is hosted, certificates to be done first, maintenance costs, what to do in case of ... and absolutely agree on the so-called "right of Monta", that is on what belongs to the owner of the "Stallone" and what to the owner of the "Fattrice" (technical terms to be used).
Generally the option of choice is up to the owner of the Stallion: if you have chosen the "partner" for reasons related to your breeder projects then you will probably be more interested in having one or two puppies (if the litter is particularly large) to add. to your farm. Otherwise you can ask for the equivalent in money.
I prefer a mixed formula when I sell the Stallone for external mount and in my contract it is written that the right to mount is increasing according to the number of puppies born, to share the risk equally.
Certainly in the contract I write that the puppies born from the mating must be sold under the same contractual conditions with which I sell them, or with the same safeguards (no shops, no pedigree, not breeding unless they accept a mentoring agreement. and so on).
Logistics
After  all the preparations made the moment finally arrives in which he and she meet: there are many good reasons why it is she who goes to his house but sometimes the opposite is also true. In fact, it seems that the male in his territory is more Macho and more self-confident, and given that females often beaten (even hard!) Putting them in a new environment makes them a little less bold, facilitating the male's task. It is also true that in an "other" environment the male may be in awe of the smell of another male who has marked that territory previously, and therefore not be in a position to concentrate on the seduction of the female.
On the other hand, often when you go to his house, or because of the distance or because of the particularly unwelcome car trip, perhaps for a too fearful character, in short, the heat may go away. If you are unwilling to leave your cat too long in someone else's house, set up an alcove with you for the next heat.
How do you prepare an alcove? Nothing special is needed, often they don't even eat or drink all the time, however only the litter box, water and food are essential. But don't be surprised if for 48 hours they will live only on love!