A video with an enormous audience is not necessarily viral, and a genuinely viral video may finish with modest total views. The two words describe different properties and the confusion between them causes real misjudgements.
Virality is a rate, not a total
The concept describes how quickly material spreads relative to the audience it began with, which is a measure of acceleration rather than of size.
Something reaching a hundred thousand people from a standing start behaves very differently to something reaching the same number through an existing large audience.
Only the first is spreading in the sense the word describes, since the second was distributed rather than transmitted from viewer to viewer.
Popularity is a stock, virality is a flow
A popular channel has accumulated an audience that turns up reliably, which produces large numbers on every upload without any spread occurring.
That is a durable asset, and it produces predictable results, but it does not extend beyond the audience already assembled.
Viral spread reaches people with no prior connection, which is why it produces sharper peaks and why it is far harder to repeat deliberately.
The decline patterns are completely different
Viral material falls away almost as fast as it rose, because the mechanism driving it is exhaustion of a susceptible population rather than sustained interest.
Popular content declines slowly, following the ordinary decay of any upload, since its audience was never expanding in the first place.
Reading a viral peak as a new baseline is therefore a predictable error, and one that leads creators to make plans against a level they will not see again.
Viral audiences convert poorly
People reached by rapid spread arrived through a single piece of material rather than through interest in its source, and most have no intention of returning.
Subscriber conversion from a viral event is consistently weaker than from ordinary distribution, because the relationship was to the clip and not to the channel.
This is why a large spike often changes very little about a channel's ongoing numbers, which creators find deeply confusing at the time.
Which one is worth pursuing
Virality is largely outside a creator's control, depending on timing and on a public mood that cannot be scheduled, and it is not a strategy that can be relied on.
Building accumulated audience is slower and compounds, since every upload reaches everyone gathered so far and adds to the base.
The reasonable position is to build for the second while remaining able to handle the first, because a spike arriving at a channel with no structure behind it converts almost none of it.