If you 'keep a look out' for something or 'keep an eye out' for something it means you are keeping watch or observing in order to find something, stay alert or to avoid danger. These are both idioms used in social and professional contexts.

1. My friends should be arriving here any minute now, so I better keep an eye out for them.
2. The soldier was tasked with keeping a lookout for enemy troops.

1. Before the students read the poem, the teacher told them to keep a lookout for hidden meanings.
2. When you're reviewing the document, please keep an eye out for any mistakes.