The JLPT has five levels: N1, N2, N3, N4 and N5. The easiest level is N5 and the most difficult level is N1.
N1 difficult ←→ easy N5
N4 and N5 measure the level of understanding of basic Japanese mainly learned in class. N1and N2 measure the level of understanding of Japanese used in a broad range of scenes in actual everyday life. N3 is a bridging level between N1/N2 and N4/N5.