A more thorough explanation:

Probative

Tending to prove or establish proof.

• The DNA evidence presented in court was probative in proving the defendant's guilt.
• The witness's testimony was probative in establishing the timeline of events.

These examples illustrate how evidence or testimony can be considered probative if it helps to prove or establish proof in a case. In other words, if the evidence or testimony is relevant and useful in proving a point, it can be considered probative.