Difficuly Class (DC) is integral to the D&D 5e platform. This article explains how it works.
While gameplaying, there is often a scenario where a player or creature will need to perform an action, require insight into a discovered item, dodge a wayward arrow, lift a heavy object etc. There are specific rules built into the platform that determine how circumstances such as these are handled.
The Difficulty Class in Dungeons and Dragons is a fundemental component that is used to determine how difficult it is to complete a specific task/challenge.
When faced with a challenge, the DM will
The assigned difficulty will range from 1 to 30 (1 being extremely easy to 30 being nearly impossible).
The ability will be selected from the range of abilities that are core to the D&D platform.
Once the difficulty has been assigned, the player will roll a d20 to determine if they can overcome the challenge. Any modifiers for the given ability will be added to the roll.
Roll + Ability Modifiers > DC ==> Success!
Difficulty class examples (page 174 Players Handbook)
Task Difficulty DC Very easy 5 Easy 10 Medium 15 Hard 20 Very hard 25 Nearly impossible 30