counter for stories; counter for episodes
Used to count stories, tales, or episodes of TV series, dramas, etc. Often follows a number or quantity word.
このドラマは全十話です。
This drama has ten episodes in total.
一話だけ見て寝ます。
I'll watch just one episode and go to bed.
The noun 話 (はなし) means 'story' or 'talk', while 話 (わ) is a counter used specifically for counting stories or episodes.
The counter 話 (わ) is derived from the noun 話 (はなし), with the reading わ being a bound form used in counting contexts.