Loshon hara literally means "evil tongue/speech." It's usually translated as "gossip," but while that's a component of lashon hara, that's not totally inclusive of the idea.
Have you thought about what gossip is? It's usually a true statement about someone else that you're not supposed to know and/or share. I don't know about you, but that's different than what I think of when I hear the word gossip. That underscores the very important idea of lashon hara that people usually talk about: just because the statement is true doesn't mean you have a free pass to say it to someone else.
The major voice on lashon hara is the Chofetz Chaim, which is the name of the book Rabbi Yisrael Meir Kagan (1838-1933) wrote about lashon hara. There is a ridiculous amount of books written on the topic of lashon hara, and I suggest that all of us should read at least one. This is a mitzvah recognized as binding by all movements of Judaism (to my knowledge), so I encourage all of you to take on some observance this week related to elevating your speech!
You'll often hear the term "lashon hara" thrown around in speech, yet there is so much actual lashon hara used in the same breath! And sometimes, that's even the topic of discussion!
A good story I once heard about the Chofetz Chaim:
He was traveling, and he caught a ride with a cart full of horse traders who spent the several hours of the trip "talking shop" about horses. The Chofetz Chaim was quiet during the entire ride. At the end, they finally realized who he was and began to apologize profusely for not realizing they had such a highly-esteemed rabbi riding with them! Then they began to apologize for talking about horses instead of "holier" subjects. The Chofetz Chaim responded, "I was just glad you weren't discussing people."I think that quote about sums up lashon hara. Avoid talking about people. And don't listen when other people do! That's why it's so hard to perfect this mitzvah!
Lashon hara has very complicated rules. They can be broken down into several categories (going from memory here):
Speech when you're unsure if it's true or not
Who the speech is addressed to
How many people the speech is addressed to
The purpose of the speech
The expected response of the listener
Now go forth and learn! And don't feel so lost in conversations!