CTA is an investment strategy (also a type that must register with the CFTC, but thats a different matter). CTAs are commonly private investment vehicles, like most other hedge fund strategies.
So the similarities (CTA is considered a HF strategy, is usually structured as a HF investment, etc) are really more than the differences. Those differences can include things like the underlyings strategy (CTAs often trade futures/swaps/etc and can be in a discretionary or systematic fashion, in things such as indices, currencies, commodities, rates). Probably the most simple version is a trend-following strategy that relies on algorithms/models for signals, I find that most references to CTAs focus on this type of strategy.
The material will probably tell you that CTAs are low/negatively correlated, very liquid, and trade very deep markets…but if memory serves me they usually mean that CTAs are a type of hedge fund (like long/short, distressed, etc)