Is the data in a data plan for upload/download (interchangeable), or only one way?

Ex: if I get a 5GB data plan, does that mean I can upload 5gbs? And if so, can I additionally download 5gbs, or does upload capacity take from download capacity?

If upload capacity has a different limit than download, where can I find what the limits are? I haven't been able to find any info on this when shopping plans.

Thanks