Used as a na-adjective to describe something or someone as pitiful, miserably inadequate, or emotionally moving in a sad way, similar to English 'pathetic'.
His excuse was pathetic.
The final scene of that movie was so pathetic that I cried.
Loanword from English 'pathetic', borrowed in the 20th century. The exact derivation is straightforward; the katakana spelling reflects the English pronunciation.