The intensity of the relationship is stronger during dating when compared to seeing someone. You tend to discuss more serious stuff during dating that shall give concrete outcomes about your future if you are going to be together, seeing someone has very casual talks and nothing serious about anything.
Is there a difference between dating and seeing someone?
Dating can mean absolute no commitment, and can refer to someones lifestyle choices. While seeing someone is usually used as a term of reference, dating can be clarified. You can be dating someone casually (or a lot of someones casually), or you can be dating exclusively.
Is dating more than one person bad?
Its not uncommon to be attracted to more than one person at the same time. But whether or not you act on those feelings wont only affect you. If you want to date more than one person, make sure that everyone involved understands this and is okay with it. Also, be sure beforehand that you can handle it.