Conversational Agent
A conversational agent, is a synonym of conversational system, a computer system intended to converse with a human in a natural language.
Let's see what wikipedia states for conversational agent:
A dialogue system, or conversational agent (CA), is a computer system intended to converse with a human. Dialogue systems employed one or more of text, speech, graphics, haptics, gestures, and other modes for communication on both the input and output channel.[1].
In common practice, conversational agent in an umbrella term generally used as synonym of chatbot, but technically a chatbot is instead a conversational system that communicate just via texts, on chat-based platforms (as instant-messaging mobile apps).
Especially in academic parlance, the term conversational agent was synonym of chatbot, and the reason emphasis on the "agent" was maybe because conversational agents was considered a special application in intelligent systems[2] or Multi-agent systems[3] research.
The term agent is probably misleading, because assimilating any conversational system as an agent that mediate between an end-user (e.g. a consumer of a business platform) and a business human operator. That's in general not true. Instead the agentive role is commonly related to a special case of conversational system that act as intermediator, requiring a final conversation with a human operator (that's commonly called, in customer service realms: human-in-the-loop). But there are many cases where the conversational system is not properly an agent, by example in pure command-and-control conversational systems that just execute automation commands to action (electro-mechanical) actuators, by example in home-automation or industrial automation realms.