4. (5 points) Definition: $m \otimes n=m \times m-n \times n$, then $2 \otimes 4-4 \otimes 6-6 \otimes 8-\cdots-98 \otimes 100=$
【Solution】Solution:
$$
\begin{array}{l}
\text { Original expression }=2 \otimes 4-4 \otimes 6-6 \otimes 8-\cdots-98 \otimes 100 \\
=\left(2^{2}-4^{2}\right)-\left(4^{2}-6^{2}\right)-\left(6^{2}-8^{2}\right)-\cdots-\left(98^{2}-100^{2}\right) \\
=2^{2}-4^{2}-4^{2}+6^{2}-6^{2}+8^{2}-\cdots-98^{2}+100^{2} \\
=100^{2}+2^{2}-4^{2}-4^{2} \\
=10000+4-16-16 \\
=9972
\end{array}
$$

Therefore, the answer is: 9972.