Which term refers to a speech or discourse that seeks to improve someone's intellect or morals?

The term "edify" specifically refers to the act of instructing or improving someone intellectually, morally, or spiritually. It derives from the Latin word "aedificare," which means to build, suggesting that to edify someone is to build up their character or knowledge. The focus on ethical or intellectual development aligns perfectly with the definition provided in the question.

The other terms do not convey this sense of moral or intellectual improvement. "Descant" refers to a discussion or commentary, often in a musical context, rather than an improvement of intellect or morals. "Descry" means to catch sight of something or to discern, while "depredate" refers to the act of plundering or robbing, which is completely unrelated to the notion of edification. Thus, "edify" is the term that fits the criteria of the question accurately.