-1' OR 5*5=26 --

This looks like a fragment of a SQL injection payload. Here’s a quick breakdown of the pieces and what they would do in a typical SQL context:

• -1' : Attempts to terminate an existing string literal in SQL. If the input is inserted into a query like ... WHERE user = '$input', this part tries to close the quote mismatched by the rest of the payload.
• OR : A logical operator to add another condition to the WHERE clause.
• 5*5=26 : A boolean expression. It evaluates to false (25 = 26 is false).
• -- : SQL comment marker. Everything after this is ignored by the SQL parser.

In a vulnerable query, the whole string could alter the WHERE clause, e.g., turning a condition into something like: ... WHERE user = '' OR 55=26 -- ... Since 55=26 is false, the effect depends on the surrounding query. If someone used a tautology like ' OR 1=1 --, the condition would always be true (bypassing checks in insecure code). With 5*5=26, it’s not a tautology, so the exact impact would depend on the rest of the query and how the database engine handles the syntax after the injection.

Important takeaway for exams and practice:

• This illustrates why parameterized queries are essential. Do not build SQL by concatenating user input.
• Defensive practices: use prepared statements/bound parameters, input validation, least-privilege database accounts, proper error handling, and (where appropriate) ORMs that use parameterization.

If you want, I can give a short, exam-style question and model answer, or show safe coding examples in a language you’re studying (Python, Java, etc.).