All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Intention, in language, means the aim. You say: I intend to travel; meaning, I decided and aimed at it. An-Nawawi : “Intention is what is heartily decided to be done whether it is an obligatory deed or not.” Also, Al-Iraqi said in Ath-thakheerah: “It is that which the human-being heartily aims to do, so it is of the wish and decision type and not of the knowledge nor of the belief type.” [Refer to Mawaahib al-Jaleel (1/230)]
For more benefit on the meaning of intention and that it does not have to be uttered, please refer to Fataawa 370540 and 167503.
Allah knows best.