In cross-coupling reactions, the component reagents are called cross-coupling partners or simply coupling partners.
These reagents can be further classified according to their nucleophilic vs electrophilic character: Typically the electrophilic coupling partner (R-X) is an aryl halide, but triflates are also used.
Nucleophilic coupling (R'-Y) partners are more diverse.
In the Suzuki reaction, boronic esters and boronic acids serve as nucleophilic coupling partners.
[1] Expanding the scope of coupling partners is a focus methods development in organic synthesis.