Cryptogram
A cryptogram is a puzzle in which a short piece of text — usually a quotation or a proverb — has been encrypted by replacing each letter with a different letter or symbol, and the solver's job is to work out that substitution and recover the original message.
The substitution is consistent: whatever stands in for E at the start stands in for E everywhere. That consistency is the whole solving method. Word spacing and punctuation are normally left alone, so a one-letter word is almost certainly A or I, an apostrophe followed by a single letter is usually S or T, and the commonest three-letter word in the puzzle is a good bet for THE.
From there it is letter frequency. E, T, A, O, I and N carry most English text, so the symbols that appear most often are worth guessing first. Doubled letters narrow things further — LL, EE, SS, OO and TT are common, while doubled consonants like JJ do not occur. Each correct guess fills in everywhere at once, so the puzzle speeds up as it goes.
A cryptogram is a cipher rather than a code: it works letter by letter, not word by word. Puzzle magazines call the version that keeps word spacing an Aristocrat, and the harder version that runs the letters together in blocks a Patristocrat.
Daily Cryptogram — a new one every day, with emoji standing in for letters.