If you maintain something, you continue to have it, and do not let it stop or grow weaker.

If you say that someone maintains that something is true, you mean that they have stated their opinion strongly but not everyone agrees with them or believes them.

If you maintain something at a particular rate or level, you keep it at that rate or level.

If you maintain a road, building, vehicle, or machine, you keep it in good condition by regularly checking it and repairing it when necessary.

If you maintain someone, you provide them with money and other things that they need.