A biaxial strained solid has stress introduced in two directions (x-y), also referred to as global strain. It can be induced by normal and shear stress at same time. You can find good information if you search for 'Material Failure Criteria', there are plenty theories about it.
this is my POSCAR and if i want to give 5% strain in the y direction then how can i give the strain in the second row ? should i change 5% of indivisual value in the second row? (i am using vasp for all calculation)