Something that's long-term has lasted for quite a while. If you have a long-term girlfriend, she's been in your life for years.
Use the adjective long-term to describe things that are so enduring that they're nearly permanent. Someone who's a long-term resident of Canada has lived there for a very long time, and news of long-term unemployment is discouraging because it means people have been out of work for months and months. Long-term was originally a word describing only insurance policies, in the 1870's.