Approximant consonant

An approximant consonant is a consonant that sounds in some ways like a vowel. For example, lateral approximants like the sound for "l" in the English word "like", the sound for "r" in the English word "right", and semivowels like the sound for "y" in "yes" and the sound for "w" in "wet" are all approximants. These sounds are pronounced by bringing two parts of the mouth, for example the tongue and the roof of the mouth, close to each other. However, it is not close enough to cause the air to be blocked, like in a fricative consonant. Also, the parts are not far apart enough to become a vowel.
Semivowels.
Semivowels are a type of approximant consonant, which sound like vowels if you pronounced them alone. However, many languages use them as consonants. Here are the common semivowels in the International Phonetic Alphabet. 
Lateral approximants.
In lateral approximants, only the centre of the tongue touches the roof of the mouth. So, air can only flow through the sides of the tongue, like the sound "l" in "like".