What is get a word in edge wise?

The phrase "get a word in edgewise" means to be unable to speak because someone else is talking constantly. It describes a situation where you're trying to contribute to a conversation but are having difficulty finding an opportunity to do so.

Here's an example:

"I tried to tell her about my day, but she was talking so much I couldn't get a word in edgewise."

The phrase implies that the other person is dominating the conversation and making it hard for others to participate.