[temp.variadic] p3

An init-capture pack is a lambda capture that introduces an init-capture for each of the elements in the pack expansion of its initializer.

[temp.variadic] p4

The number of elements of an init-capture pack is the number of elements in the pack expansion of its initializer.

So, what does "pack expansion of its initializer" mean? We just define that

A pack expansion consists of a pattern and an ellipsis, ...

A pack whose name appears within the pattern of a pack expansion is expanded by that pack expansion.

In a capture-list ([expr.prim.lambda.capture]); the pattern is the capture without the ellipsis.

For example

template <typename... Args>
void foo(Args... args) {
    [...xs=args]{
        bar(xs...);             // xs is an init-capture pack
    };
}

...xs=args is a pack expansion where xs=args is the pattern, we say the pack args is expanded by this pack expansion; =args is the initializer in the init-capture pack. We never define "pack expansion of its initializer". This utterance is obscure in the current draft. Since we say:

An init-capture containing an ellipsis is a pack expansion that declares an init-capture pack

A pack expansion consists of a pattern and an ellipsis, the instantiation of which produces zero or more instantiations of the pattern in a list (described below).

thus, shouldn't we say

An init-capture pack is a lambda capture that introduces an init-capture for each of the elements that resulted from the instantiation of the init-capture that declares it.

?

As well as

The number of elements of an init-capture pack is the number of elements that resulted from the instantiation of its pack expansion.