A long-standing thing is not new. It has been there for a long time: a long-standing tradition, a long-standing agreement, a long-standing problem, a long-standing friendship. The idea is that it has been in place — a custom people have kept, a deal that has lasted, a complaint nobody has really cleared up. It does not by itself say the thing is good or bad. A long-standing custom can be loved or quietly hated. The word sounds a little serious, the kind you meet in news and careful speech, but people use it in everyday talk too. It is close to long-running, though actually they do not sit in quite the same places. Long-running likes things that keep playing out, like a show or a dispute. Long-standing likes things that have simply existed: a relationship, a rule, a habit, a grudge. You almost always see the hyphen, and it almost always comes before a noun.