Algorithmic trading involves the use of algorithms to optimally execute trading instructions. Then there are algorithms which initiate trades, based on various quantitative strategies (e.g. pairs trading).
I have the impression that "algorithmic trading" (or automated trading) is often used for both types of algorithms, although they're very different. They can be used exclusively (a human executes the trading instruction of an algorithm, or a human manually inputs a trade which the trading algorithm executes) or together sequentially (the latter algorithm submits trades to the former, which executes them). So how do we distinguish these two types of algorithms?