Currently, the leading blockchain networks like Bitcoin or Ethereum are facing scalability issues due to the increasing number of transactions and technical limitations, resulting in lower transaction speed and higher transaction fee. Layer 2 technologies were developed to solve such issues.
Layer 2 refers to another blockchain network, sometimes referred to as sidechain. It is built to record and confirm minor transactions in order to reduce burdens from the main network or mainchain. After transactions are confirmed on Layer 2, it will then make the summary of transaction records before sending them to the mainchain in regular intervals.
Immutable X is one of the Layer 2 or sidechains of Ethereum, but it is built to specifically support transactions that are related to NFTs.