Can you tell me what mDNSResponder is?

Can you tell me what mDNSResponder is and why, according to Activity Monitor, it shows continual use of my satellite internet bandwidth? In the past couple of days, I have noticed a steady up and down loading of packets on Activity Monitor (about one MB per minute) which will soon cause me to exceed my 10GB monthly allowance. This is a change from previous behavior?

thank you,

Joe