1. The user is asking about the fourth power of the variable $y$, written as $y^4$. 2. The expression $y^4$ means $y$ multiplied by itself 4 times, i.e., $$y^4 = y \times y \times y \times y.$$ 3. This operation is called raising $y$ to the fourth power or taking the fourth power of $y$. 4. For example, if $y=2$, then $$y^4 = 2^4 = 2 \times 2 \times 2 \times 2 = 16.$$ 5. So, the power of 4 applied to $y$ indicates multiplying $y$ by itself four times. 6. If you want to compute or simplify an expression with $y^4$, please provide the full expression or context. 7. If "y'''" means the third derivative of $y$ with respect to a variable, and you want to find its fourth power, that would be $(y''')^4$, meaning you raise the third derivative of $y$ to the power of 4. Final answer: The fourth power of $y$ is $y^4$.