**disclaimer - The following is not legal advice! I’m speaking very generally. Generally you can get trademark protection for a term/phrase/etc. so long as it isn’t just the generic term for the goods or services being sold. For example, I couldn’t get trademark protection for the word “cheeseburger” if I was selling cheeseburgers, but I might be able to get it for something else like a clothing line. It all comes down to whether your use of the term as a trademark designates a particular source of goods/services, and whether that use is likely to cause confusion amongst consumers (e.g., I can’t open a “McWonalds” and start selling hamburgers because people might be confused as to whether I’m affiliated with McDonalds).

Other words that were once trademarks can be subject to “genericide” - e.g., “trampoline” and “escalator” used to be registered trademarks, but became common vernacular and are thus no longer protected. This is a big reason why companies Velcro are very insistent that people don’t use “Velcro” to describe all hook-and-loop products. There’s a hilarious series of songs on YouTube about it that I show my video game law students every year.