This is a good question. Many patent attorneys will refer to your idea as "the invention" or "the present invention". This should be okay but I like to be a little bit careful when using this term.
The reality is your invention may be different things. For example, if your invention is a chair that may have 3 legs or 4 legs you do not want to write "The invention is a chair that has 3 legs". It would be better to write "In some embodiments, the present invention chair comprises 3 legs while in an alternative embodiment the chair comprises 4 legs"
Note I am not referring to the "invention" and instead describing the chair.