-1" OR 5*5=25 --

That looks like a classic SQL injection payload.

Breakdown:

• -1" ends a string literal in many SQL dialects.
• OR 55=25 is a boolean expression that evaluates to true (since 55 = 25).
• -- starts a comment in SQL, so the rest of the line is ignored.

Effect in a vulnerable query:

• If inserted into a string context like: ... WHERE user = "-1" OR 5*5=25 -- ... the condition evaluates to true, potentially bypassing checks (e.g., authentication).

Defensive lessons (exam prep and real-world):

• Use parameterized queries / prepared statements (do not build SQL by string concatenation).
• Validate and sanitize inputs; treat numeric fields as numbers, strings as strings with proper escaping.
• Prefer ORM/query builders that bind variables safely.
• Implement least-privilege database accounts and proper error handling to avoid exposing details.
• Consider input-length/format checks and disable dangerous SQL features if possible.

If you want, I can tailor explanations or example questions for your specific exam topics (SQL injection, boolean logic, or secure coding practices).