Diphthongs are types of vowels where two vowel sounds are connected in a continuous, 

gliding motion. They are often referred to as gliding vowels. Most languages have a number of

diphthongs, although that number varies widely, from only one or two to fifteen or more.

Examples:

ai - hide, like, Mike, my, life
ei - make, take, lake, eight, weight
ou - go, motion, own
ie - here, really
ea - there, hare, bare
au - mountain, amount, cow