In genealogy and wills, a person's issue means all their lineal descendants.
[1] Issue is a narrower category than heirs, which includes spouses, and collaterals (siblings, cousins, aunts, and uncles).
[2] This meaning of issue arises most often in wills and trusts.
[3] A person who has no living lineal descendants is said to have died without issue.
A child or children are first-generation descendants and are a subset of issue.