When configuring your app, you often have the option to choose a Custom Value instead of a column value. This means you can manually enter a static value in that field.
You may see the option to enter a custom value when configuring Components. When you manually enter a custom value, it will be the same every time it appears and won't change when the data in your sheet or table changes.
The value you test for in a condition defaults to an empty field where you can enter a custom value. Depending on the condition's context, you may see Column Values, User Profile Columns or Screen Values in this menu.
If you use a custom value in the filter condition, then it will only return items that contain the custom value you are filtering for.