A tongue-twister is a phrase in any language that is designed to challenge the speakers of proper articulation. Many tongue-twisters have two or three sequences of sounds, then the same sequences of sounds with some sounds exchanged, e.g. "she sells / sea shells".
Some tongue-twisters are specifically designed to cause the inadvertant pronunciation of a profanity if the speaker stumbles verbally.
Something that might be regarded as a type of tongue-twister is a shibboleth, that is, a phrase in a language that is difficult for someone who is not a native speaker of that language to say. An example is Georgian baqaqi ts'khalshi qiqinibs "a frog in water jumps", in which "q" is a sort of gulping sound.
For examples, see list of tongue-twisters.