It describes something that grows or builds up by adding successive amounts.
Here are some examples:
* Cumulative effect: The long-term impact of something, which grows over time.
* Cumulative debt: The total amount of debt owed, including the interest accumulated over time.
* Cumulative rainfall: The total amount of rain that falls over a period of time.
Essentially, anything that builds up or adds on to itself over time can be considered cumulative.