Usage notes:Avoir l’air is a ubiquitous French expression for describing the appearance of a person or thing. It’s structurally similar to the English "to have an air of" but is more general and far more common. Avoir l’air may be followed by an adjective, noun, or verb.
Avoir l’air + adjectif = To look (adjective)
Ça a l’air delicieux !
That looks delicious!
Ta fille a l’air triste.
Your daughter looks sad.
Cet immeuble avait l’air miteux.
That building looked seedy.
Agreement with avoir l’air
The adjective needs to agree with the subject when the adjective is modifying him/her/it. However, when the adjective is modifying the word air itself, the adjective remains masculine singular to agree with it.
Cette femme a l’air heureuse.
That woman looks happy (looks like she is happy).
Cette femme a l’air accueillant.
That woman looks welcoming (has a welcoming look).