what does the term half link mean?

Answer 1

unless you happen to be talking about bycycle chains, I think the term you are asking for must be "half-life" -- it is the amount of time it takes something like radiation levels to decrease by half -- e.g. if there was a reading/level of 100 and it had a half life of 1 month, the reading level would be 50 after month 1, 25 after month 2, then 12.5, 6.25, 3.125, 1.5625.....