This is a tracker weak aura that quickly shows you which external cool downs are on you at any moment during group content.
This will show you which buff you have active, who cast the buff on you, and how long is remaining on said buff.
If you would like to make the icons larger you can click on the "External Cooldown On You Tracker" weak aura group and then click on the "Display" settings near the top. After that, under "Position Settings" you can adjust the Width/Height settings to whatever size works best for you.