Semiessential amino acid is:
Essential, semiessential and non essential amino acids.

Essential: Those amino acids which cannot be synthesised in the body. Hence these amino acids are to be supplied in the diet. 
Semiessential: Growing children require them in the food, but not essential in adults. 
Nonessential: Amino acids which can be synthesised in the body, hence not required in the diet.
Arginine
Lysine
Glycine
Phenylalanine