Why do we use the term 'half life' for proteins?
Here is a link to some information regarding this question, but I am unable to infer it.
"Half-life time" is a general term. This is a time after which the amount of substance X decreases by 50%.
If you take a bulk of something (say, 100 protein molecules), if this protein has half-life time of 1 hr, then 1 hr later you'll have 50 molecules left.
In cellular biology it usually means that 50% of protein got recycled/degraded in given half-life time