From the Urban Dictionary:
Too Long. Didn't Read.
Frequently used acronym by lazy, ignorant people in Internet Forums, where their urge to type something exceeds their ability to read something or if they generally lack
semantic ability to either comprehend or respond to a post due to underdeveloped brain.
Stating that they were to lazy reading someone else's post just confirms
the ignorant attitude and also often destroys the discussion in the thread.
The average IQ of people typing TLDR in Internet forums is about
64.