Daily median block weight. Weight is a measure of the size of bitcoin blocks including the segwit discount. Weight = (tx size with witness data stripped) * 3 + (tx size). Each block has a limit of 4M weight units or 1M vbytes (1 vbyte = 4 weight units).
Unit:  Weight units (or 1/4 vbytes)
Source:  BitcoinVisuals node (bitcoind)Learn More