LOS vs NLOS

Line of Sight (LOS)

Straight visibility between a transmitter and a receiver. There is not any obstacle between devices which could interfere (to get a comprehensive understanding please have a look at L2 Site Survey – Fresnel Zone).

Non-line of Sight (NLOS)

Straight visibility is obscured (partially or completely) by obstacles, thus making it difficult for the radio signal to pass through.