What is RingCT (Confidential Transaction) (Monero)?

Ring Confidential Transactions (RingCTs) are a mechanism used within the Monero blockchain platform which allows the amount in a transaction to be hidden, similar to now the system's ring signature mechanism obfuscates the details of sending and receiving addresses. RingCTs drastically improve the unlinkability and untraceability of transactions within the Monero network by allowing for ring outputs of various transaction sizes, without compromising the anonymity of the transaction. This function was added to Monero in January of 2017 and made mandatory on the network in September 2017.