Consolidation is when you take lots of individual small amounts of BTC and turn it into a single BTC transaction (called a UTXO - Unspent Transaction Output).

As fees are charged against individual amounts, when mining fees are low, you can consolidate your BTC into a single transaction output, so that when fees are high, spending BTC is cheaper in fees.

However, a user on Xitter suggested that an employee at the OKX exchange fucked up and started consolidating and then flooded the network with transactions each out bidding the previous transaction in fees, bumping fees into the $50 range, meaning that his consolidations were costing about a third of the value in fees.