A link exchange happens when two website owners or webmasters come to an agreement to post each other's links in their respective publications. Although this used to be common practice in order to improve SEO, the current efficiency of the process is under question.
A link exchange is the process through which a website owner agrees to post a link to another website, in exchange for the owner of that website doing the same for a link of the initial website owners’ choice. The purpose of this exchange between webmasters is, most of the time, to increase the domain authority of both websites involved. A secondary benefit can be getting an additional source of referral traffic.
The placement of the links and other details surrounding the exchange are entirely based on the negotiation between the two parties involved. There is no rule that governs link exchanges.
Link exchange used to be very common in the past, when webmasters realized that the number of backlinks was an important criteria for search engine algorithms. But since this type of cross-promotion would often be abused and would many times lead to “link schemes”, the impact that it has on SEO has decreased. There is still some debate whether applying this strategy is effective or not, but most experts agree that if you decide to do a link exchange, you should at least consider the relevance and authority of those you are doing the exchange with.
On the other hand, there is little to no interest at all for a website with high authority to accept a link exchange with one that belongs to a domain with lower authority. This is why a link exchange is more likely to happen between websites that are more or less on the same level in terms of authority. That, in and of itself, may raise the question if this sort of linking is beneficial.