Literal support means that the words of the claim are identical to words in the description. It does not have any particular nuanced meaning.
The purpose of that presentation is to demonstrate that the requirements for written description in the US go far beyond literal support. That is, even if the claims are replicated in the description, that is not enough to satisfy the written description requirement (or indeed, the enablement or best mode requirements).
In fact, the presentation you link to includes a nice quote from In re Kaslow, 707 F.2d 1366, 217 US PQ 1089 (Fed. Cir. 1983):
The test ... is whether the disclosure of the application as originally filed
reasonably conveys to the artisan that the inventor had possession at that time of the later claimed subject matter, rather than the presence or absence of literal support in the specification for the claim language.
Literal support therefore does not have much place in US law.
However, historically, countries inheriting their patent system from the UK had a requirement for fair basis, where the claims had to be fairly based on the description. For example, the now superseded Patents Act 1949 (UK) s 4(4) provided:
The claim or claims of a complete specification must relate to a single invention, must be clear and succinct, and must be fairly based on the matter disclosed in the specification.
This was a low bar, and literal support (where the wording of the claims are identical to words in the description) would be sufficient (though not required). This gave rise to the practice of having consistory clauses, where the claims were literally copied into the summary of invention section. However, most (or possibly even all) countries have moved on to a support requirement now. Yet the practice of consistory clauses lives on.
Literal support also appears in some guise in European law. Art 123(2) EPC provides:
The European patent application or European patent may not be amended in such a way that it contains subject-matter which extends beyond the content of the application as filed.
This is often imprecisely glossed as a requirement that the wording of an amendment must appear verbatim in the description as originally filed. That is, an amendment is generally allowable if it has literal support in the application (and does not otherwise impermissibly combine embodiments and the like). In practice though, literal support is only one factor for compliance with Art 123(2) EPC, and is neither necessary nor sufficient on its own.