Complex sentence: DR, short for "too long; didn't read", is Internet slang to say that some text being replied to has been ignored or as a signifier for a summary of an online post or news article.
Split into simpler sentences: DR, short for "too long; didn't read", is Internet slang to say that some text being replied to has been ignored. It is also used as a signifier for a summary of an online post or news article.