The inequality \( x \leq -1 \) indicates that \( x \) can take any value less than or equal to \( -1 \).
Given the range between \(-4\) and \(-5\), we can analyze this interval:
- The interval from \(-4\) to \(-5\) is actually from the larger number \(-4\) (not including \(-5\) since the interval does not specify it) down to just above \(-5\).
Thus, the numbers in this range can be expressed as all values in the form of decimals (e.g., \(-4.0001, -4.0002, ...\) down to values approaching \(-5\)), which is a continuous range of numbers.
Since there are infinitely many decimal numbers in any interval on the real number line, between any two real numbers (even as close as \(-4\) and \(-5\)), there are infinitely many solutions.
Therefore, the correct answer is:
an infinite number.