If you're looking to swap your Lycra for baggy mountain bike shorts, you'll often see terms such as inner shorts and outer shorts. It may seem nonsensical to wear two pairs of riding shorts, but it's not all that different from your undies and your regular pants.
The inner shorts or liner will be tight-fitting, made from highly wicking breathable fabric, and feature a chamois pad to protect sensitive areas – however comfortable your best MTB saddle is, chances are you'll feel the benefit. Inners and liners come in both shorts and bibs, and some have pockets in strategic areas for extra gear stashing.
Most outer shorts are BYO liner and this is because – as with most questions of what to wear mountain biking – everybody has their personal preference.
You can also wear standard road shorts or gravel bike bib shorts here, too, but they don't breathe quite as well. Some shorts do come with a short liner, but we've often found that included inner shorts will be of lesser quality, especially in the chamois and fit.