run-on sentence

Short definition from Wiktionary

Noun

1. 1
   A written sentence that inappropriately joins two (or more) independent clauses into a single sentence, often with only a comma as separator (comma splice), which should be rendered either as separate sentences or as clauses joined more appropriately (such as by a semicolon or by a comma and coordinating conjunction).
2. 2
   Any very long, often also in other ways badly formed or even chaotic sentence.