What digital code consists of elements having unequal length?

Varicode is a digital character encoding system used extensively in amateur radio digital modes, most notably PSK31. It is specifically designed to use elements of unequal length to maximize transmission efficiency. Similar to how Morse code assigns shorter dot-dash sequences to common letters like 'E' and 'T', Varicode assigns shorter bit sequences to the most frequently used characters in the English language, while rare characters get much longer sequences. In contrast, codes like Baudot and ASCII are fixed-length codes. Baudot uses exactly 5 bits for every character, and standard ASCII uses 7 bits, regardless of how often the character appears in normal text.