An item that's mulled over has been thought about thoroughly or carefully. You often hear this word used when talking about decisions or plans.
When someone says their decision was "mulled over", it means they really considered their options and weighed all the pros and cons before making a choice. This can happen in business, when a company is deciding whether to invest in a new project for example, but it's also something you hear when friends are talking about a big life change like moving or getting married. A person might say "I've been mulling over what kind of car to buy" which means they're really thinking about all the possibilities and trying to make up their mind. It's a nice way to talk about taking your time and being careful when making decisions, rather than just jumping into something without thinking it through.
simple past and past participle of mull
