Subagent vs Agent
The general concept of a tool-using loop, versus one specific dispatched instance of it
Agent
The broad concept: a model wired to tools and a loop, able to act, observe results, and decide what to do next. Every subagent, worker agent, and orchestrator in this glossary is a variant of this idea.
Subagent
A specific kind of agent: one dispatched by another agent, given its own context window, to handle a scoped task and report a result back. A subagent is always an agent, but not every agent is a subagent.
Which one do you actually need
Agent is the category, subagent is one specific role inside it, defined by how it's dispatched and where its context lives. Ask whether an agent was spawned by another agent for a bounded task and reports back with a result, if so, it's fair to call it a subagent specifically. If it's operating independently rather than dispatched, agent is the more accurate word.