Most and Least Significant Bit

Every binary number is built from bits, and the two bits at the ends of the number have special names. The most significant bit (MSB) sits at the far left of the number, in the column with the biggest place value. The least significant bit (LSB) sits at the far right, and its place value is always 1.

Why the names make sense

"Significant" here means how much the bit is worth. In the 8-bit number 10110010, the bits sit in the columns 128, 64, 32, 16, 8, 4, 2 and 1. The 1 at the far left is worth 128, so it is the MSB. Changing that bit from 1 to 0 takes 128 away from the total, which is the biggest change any single bit can make. The 0 at the far right is worth 1, so it is the LSB, and switching it from 0 to 1 changes the total by just 1.

Shorter numbers

The names follow the position of a bit, not the digit itself. In the 4-bit number 0110 the place values are 8, 4, 2 and 1, so the 0 on the far left is worth 8 and is the MSB, while the 0 on the far right is worth 1 and is the LSB. Written with leading zeros as 00000110 the value is still 6, but the MSB is now the leftmost of the eight zeros, worth 128, because that is the bit sitting in the biggest column. So the MSB is always the leftmost bit, even when that bit is a 0.