Howard Schiff Law office suing me for credit card debt

I had to default on a credit card 3 years ago (due to increased medical bills). I was living on child support then and now and that is my only income. I just received summons/suit re this $8,000 credit card debt from Atty Schiff's office. I see people asking if "validation" of the debt was requested. What does that mean? What is the point of validation (is it a delay tactic, or other purpose)? What does DV mean? I only have child support to live on of $1,075 a month and that is over in 13 months. I'm scared and would appreciate any advise. I did not file for bankruptcy because I couldn't afford it and would rather not. Thank you.