Ever get a great idea for a name or phrase, only to find out it's already taken? Everybody has. We're just in an industry where that comes up all the time.
If you find yourself needing to know if a company or product name is legally available, or a tagline (or other patented phrase), a great resource is the US Patent Trademark Office's electronic search system, or TESS.
Select the "Basic Word Mark Search" and type in the word or phrase you're searching, and away you go! You'll want to search both live and dead trademarks (meaning both active and expired); if something comes up (and it always does), there are lots of considerations around industry, geography, category, etc that go into these things. But it's a good start, and helps prevent a lot of heartbreak and/or legal fees.
(Note that legal is just one type of name availability; also consider who "owns" the word/phrase as a URL, or the first page of results on Google.)
Name availability questions just come with the territory of being in the ideas business. So if you've got any, ask away.