Acidity of BF3 can be explained on the basis of: 

1. Arrhenius concept

2. Bronsted Lowry concept 

3. Lewis concept

4. Bronsted Lowry as well as Lewis concept

Hint: BF3 accepts lone pair from base.

Explanation: 

GN Lewis in 1923 defined an acid as a species which accepts an electron pair and base which donates and electron pair. As BF3 is an electron deficient compound, hence, it is a Lewis acid and it accepts electron from lewis base