Others already explained what it actually refers to.

The earliest use I can find for the term "seed" is in 1958. Though this doesn't concretely define the term, so it's possible that it was already a known term at that point, and originated from even earlier.

In 1958, The Cornell Research Simulator by Richard W. Conway, Bruce M. Johnson and William L. Maxwell:

0937 is the random number seed for read.

In 1961, Some Problems in Queue Simulation by Scott Garney Lewis:

Seed for arrival dist'n random number generator

In 1965, On-line Computation and Simulation: The OPS-3 System by Martin Greenberger:

To initialize the random-number generator to 3597, the user executes the SEED operator as follows: ...

The discontinued IITRAN programming language created in the mid-1960s also had a "seed" keyword, as noted in Communications of the ACM, volume 12(10), Oct 1969 (and elsewhere):

.SEED Seed for random number generator

Pseudorandom number generator (PRNG) originate from before 1958: The Lehmer generator was published in 1951. The middle-square method was described in 1949 (originating from the 1240s). But they didn't use the term "seed" in their initial publications.