Evaluate the following expression. \[ \log _{2}\left(\frac{1}{2}\right) \]

Step 1 ：Evaluate the following expression: \(\log _{2}\left(\frac{1}{2}\right)\)

Step 2 ：The logarithm base 2 of 1/2 is asking the question: '2 to what power equals 1/2?'

Step 3 ：We know that 2 to the power of -1 equals 1/2.

Step 4 ：Therefore, the answer should be -1.

Step 5 ：Final Answer: \(\boxed{-1}\)