The Thermal Design Power (TDP) is the average maximum power a processor can dissipate while running commercially available software. TDP is primarily used as a guideline for manufacturers of thermal solutions (heatsinks/fans, etc) which tells them how much heat their solution should dissipate.
If motherboard has a max TDP of 80w in this particular case, then using a CPU with TDP above that could damage the motherboard from too much thermal heat.