Multisignature (MultiSig) refers to requiring more than one key to authorize a Bitcoin transaction. It is generally used to divide up responsibility for possession of bitcoins.
A multisignature address is an address that is associated with more than one private key. The simplest type is an m-of-n address - it is associated with n private keys, and sending bitcoins from this address requires signatures from at least m keys. A multisignature transaction is one that sends funds from a multisignature address.
It is possible to use Multisignature transactions with Trezor device however it is not implemented in Trezor Wallet yet. See this blog to learn more about using Multisignature transactions with Trezor.
See also Apps:Electrum