Are fjords and cliffs the same thing?

No. A fjord and a cliff are not the same thing. A cliff is defined by Google’s define function as “a steep rock face, especially at the edge of the sea.” A fjord, on the other hand, is defined as “a long, narrow, deep inlet of the sea between high cliffs... typically formed by submergence of a glaciated valley.”

For a good example of this, think of the kingdom of Arendelle from Frozen. When Elsa freezes the body of water to go to the mountains, one of the comments Anna makes is “the fjord…”. She froze the fjord and climbed the cliffs to make her ice palace.

Disney example aside, the Cliffs of Dover are famous in England. Norway is famous for its many fjords.