Head Loss is defined as:
1. To move a given volume of liquid through a pipe requires a certain amount of energy. An energy or pressure difference must exist to cause the liquid to move. A portion of that energy is lost to the resistance to flow. This resistance to flow is called head loss due to friction.

OR

2. When she doesn't finish sucking on yo dick when she be giving you a blowjob so now you have blue balls which sucks.

A buzz word being used to refer to creators and influencers forming or encouraging unhealthy relationships with their fans. Usually used in the context of young audiences feeling they have a relationship with the influencer due to the huge amount of the influencer’s content they consume. The influencer in question, however, is unaware of the fan’s existence other than the general knowledge of having fans. Common examples include Dream and his stans. These relationships are exacerbated by the influencers confirming they have more than a creator-to-viewer relationship.

The word is circulating due to various YouTube essays about the phenomenon using the word, and therefore people who enjoy complaining about influencers repeating what they heard in the video in any comments section they can find.

When you're incensed to such an extent that your head is literally gone and all rational activity is replaced by rash, emotional decisions.