I think people use "entry level" synthetic as a way to define store-brand synthetics and the cheapest option available from a manufacturer (with some caveats).
Pennzoil Synthetic black label is the "most basic" "synthetic" that Shell offers in that line, it says Synthetic and meets API SP and GF-6. No other certifications. Is that bad? No, but it's "entry" level. Next you can "step up" to something like Pennzoil Platinum which is a Synthetic, API SP, GF-6, and has Dexos and other certifications.
The caveat here is many also say AmazonBasics/Kirkland/Supertech synthetics are "entry" level, but Platinum no better certifications and I'm not sure anyone would call Platinum entry level. Another caveat to my original statement is something like Valvoline, where their "entry-level" synthetic is their regular Valvoline Synthetic (used to be SynPower), which has Dexos1 approval, and therefore is not entry level (as the Pennzoil black label does not have Dexos1 approval). Castrol also offers a 0W-20 synthetic blend w/o Dexos1 approval. Many consider Mobil 1 Extended Performance 0W-20 to be a top tier synthetic, but judging by certifications it is no better than Supertech 0W-20.
In my opinion, I think an entry-level synthetic is a Synthetic that meets the bare minimum specifications. This is Pennzoil black label and the Castrol I mentioned above (even though I think it's marketed as a blend, but is likely a very good "blend" to be a 0W-20 non-synthetic).