In an emoji ZWJ sequence, what does the abbreviation ZWJ stand for?

In an emoji ZWJ sequence, ZWJ stands for Zero Width Joiner.

The zero-width joiner is an invisible Unicode character that can connect adjacent emoji characters into a single displayed design. Its code point is U+200D, and it has no visible width when rendered normally.

Emoji sequences using ZWJ allow platforms to represent concepts that are not assigned one standalone character. Examples include family combinations, professions with gender presentation, and some animals or objects made from multiple components.

A ZWJ sequence is not guaranteed to appear identically everywhere. If a system lacks support for the sequence, it may display separate component emoji instead. This is why a combined emoji can appear as several symbols on older software.