By "Barrier", I mean as in summoning a wall object that players cannot bypass through unless broken or circumnavigated. It could be used to block line-of-sight, or inconvenience players with an obstacle in their path. Both defensive and offensive use, has no damage, debuff or buff properties. It could also be a double-edged sword with improper use.
Most widely seen in powers themes of Ice, Earth, and Force-field users.
I recently started playing an MMO called SMITE where I saw these type of abilities in action. I was quite impressed at how simple the ability concept was and how useful it could be, without it even being considered overpowered. At most I could blockade about 3 players if they were standing right next to each other, and it only lasted at most 10 seconds. However, I usually used it to section out stragglers to prevent their group-mates from being able to provide easy-aid and for my team to close-in on them.
Other References: Green Lantern (Justice League), Raven (Teen Titans), Terra (Teen Titans), Earth Benders (Avatar), Water Benders (Avatar), Violet (Incredibles) . . .