AI Service (as used in the context of Eric Drexler's technical report Reframing Superintelligence: Comprehensive AI Services as General Intelligence) is an AI system that delivers bounded results for some task using bounded resources in bounded time. It is contrasted with agentic AGI, which carries out open-ended goals over an unbounded period of time.
A gradual accumulation of increasingly competent services is one model of how AI might develop. For a summary, see this post.