BE and LE stand for big endian and little endian. In big endian, the most significant byte is stored in the smallest address, and in little endian, the least significant byte is stored in the smallest address. That being said, endian does indicate the byte order. You can see the pattern in one of the examples in the documentation:
var buf = new Buffer(2);
buf[0] = 0x3;
buf[1] = 0x4;
buf.readUInt16BE(0);
buf.readUInt16LE(0);
// 0x0304
// 0x0403