Climbing in a gym is different than climbing outdoors in a number of ways, one being indoor bolts are in a controlled space and checked regularly.
Outdoor bolts differ from area to area and are almost always drilled by different climbers.
There are a number of types of bolts, but most fall under the categories of expansion or glue-in.
While popular crag routes have enough traffic that loose or broken bolts are discovered and replaced, untraveled and rarely-climbed lines might have bolts that are not safe to fall on.
A few reminders for summer are to bring a wrench to tighten any loose bolts and to have a few extra hangers to add to hanger-less bolts in the rock.
Watch these two short videos about how to check to see if bolts are safe.