Is having a tight ACL a good thing?

I just went to the doctor today because I've had constant knee pain my entire life. He said I could have one of three things and as he was explaining them to me he said something about my ACL being tight. Basically I could have tendinitis, a tear in my meniscus, and I have a ligament that I shouldn't. I've been researching but so far I haven't found any good explanation of a tight ACL.