I'm reading the book "Introduction to Lie Algebra and Representation Theory - J. E. Humphrey", I have a question on an example on the page number $2$. That is
Example: For reference, we write down the multiplication table for $gl(n, F)$ relative to the standard basis consisting of the matrices $e_{ij}$ (having $1$ in the $(i, j)$ position and $0$ elsewhere). Since $e_{ij} e_{kl} = \delta_{jk} e_{il}$ it follows that: $$[e_{ij}, e_{kl}] = \delta_{jk} e_{il} - \delta_{li} e_{kj}.$$ Notice that the coefficients are all $1,-1$ or $0$; in particular, all of them lie in the prime field of $F$.
My question: What is the meaning of the notation $\delta$ here?