I don’t hear chain much. I hear train though, like a forward air train by bowser or wolf carrying across the stage (typically escapable if you react correctly). A true combo is a combo that doesn’t let an opponent out of hit stun before they are hit by a follow up attack, meaning they can’t escape. Some true combos can be escaped with good DI/SDI, and are only true without DI or with bad DI. If it’s just called “combo” it’s probably referring to a series of attacks that were close together time wise but were not necessarily “true” in that the opponent had an opportunity to escape (even without proper DI) but perhaps picked a bad option or got read. Something like Ness drag down fair to run up grab isn’t true, but works a lot because people hold shield often after the drag down fair.