Comma splices occur when two complete thoughts are joined together with just a comma but no linking word (e.g. ‘and’ or ‘but’).

• I was late for class, I had a good excuse.
• I don’t like the IELTS reading test, there isn’t enough time.
• Learning vocabulary is essential, it gets easier with practice.

Comma splices can be avoided by (a) separating the two thoughts with a full stop (b) using a suitable linking word or (c) using a semi colon. For example:

• I was late for class. I had a good excuse.
• I don’t like the IELTS reading test as there isn’t enough time.
• Learning vocabulary is essential; it gets easier with practice.

NOTE: make sure you have followed the advice in the punctuation lesson regarding the use of semi colons in this manner.