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Line-in recording is a term often used by manufacturers of sound equipment to refer to the capability of a device to record 
The common 3.5 mm line-in connector has the left channel on the tip and right channel in the middle. The port is used to connect with other devices. Line-in is most commonly used for instruments.
line level
Line level is the specified strength of an audio signal used to transmit analog audio between components such as CD and DVD players, television sets, audio amplifiers, and mixing consoles.
Line level sits between other levels of audio signals. ...
audio feeds. Microphone
A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public ...
and instrument inputs, by contrast, are designed for devices which require further amplification to be at line-level.
The common 3.5 mm line-in connector has the left channel on the tip and right channel in the middle. The port is used to connect with other devices. Line-in is most commonly used for instruments.
References
Audio engineering {{Sound-tech-stub