What describes an assembly of three or four vertical studs tightly nailed together?

The assembly of three or four vertical studs tightly nailed together is accurately described as a stud cluster. Stud clusters are often used at corners, doorways, or where additional load-bearing capacity is needed, providing extra strength and stability to the frame of the structure. This arrangement helps to support loads from beams or trusses and aids in transferring weight down to the foundation.

Corner bracing typically refers to diagonal bracing added to corners to increase structural stability, rather than an assembly of vertical studs. A corner post specifically refers to a singular vertical member that might be found on the corner of a structure but does not encapsulate the multiple members represented in this question. A support beam is a horizontal member that transfers loads from above down to vertical supports; it is not an assembly of vertical studs.

Given the context and definition of each term, a stud cluster aligns perfectly with the description provided in the question, because it specifically highlights the tightly grouped assembly of vertical studs.