Airbnb's (NASDAQ:ABNB) recovery from the trough it was in at the onset of the pandemic is gaining momentum. Last spring, the company saw its revenue decline substantially as travel nearly came to a halt. Fortunately, vaccines against COVID-19 continue to be administered around the world and that is giving more consumers the confidence to book travel again. 

Based on what it's seeing, Airbnb management is expecting a rebound of epic proportions. That's understandable, considering how many people had been self-isolating for roughly 18 months now partly from government-imposed temporary lockdowns and partly from personal caution.

The clue to Airbnb management's optimism is found in a number -- $6.3 billion -- from its most recent earnings report. It's also potentially Airbnb's most important number right now. Let me explain. 

Two people unpacking luggage.

Airbnb has $6.3 billion in funds held on behalf of customers, indicating a surge in upcoming travel. Image source: Getty Images.

An upcoming surge in travel

In Airbnb's fiscal second quarter (its most recent), the company reported $6.3 billion in funds receivable and amounts held on behalf of customers. That's the amount of value in booked reservations on its site for upcoming travel that has not yet been experienced. It exists on the balance sheet because most folks book their travel several weeks to several months ahead of their intended travel dates.

The good news for Airbnb is that the total is higher than for any quarter in fiscal 2019 (before the pandemic onset). In fact, it's 43% higher than in the highest total in 2019, which also happened to be Q2.

That's a pretty valid reason for management to be optimistic about Airbnb's near-term (and potentially long-term) prospects. Customers are booking stays on the company's platform at levels higher than before the pandemic even though the pandemic is nowhere near ending. If this is what the pent-up demand is like for travel while a deadly virus is still in circulation, imagine the uncoiling when the world finally gets control of the virus. 

A reopening stock 

Airbnb is the quintessential reopening stock. The company will thrive as economies reopen and travel restrictions are lifted. Even though the direction of that trend is toward reopening, many restrictions remain. International or cross-border travel, in particular, is far below pre-pandemic levels for a host of reasons, including vaccine requirements, proof of a negative COVID-19 test, and mandatory short-term quarantines. It's likely that a significant portion of the advanced bookings right now are within the United States, where travel between states is far less restrictive at the moment, especially for unvaccinated individuals. 

Investors interested in stocks with ties to the travel industry like Airbnb should keep in mind that these companies will not be operating at full strength as long as the virus is in circulation at pandemic levels. Still, the fact that Airbnb is generating record values of reservations despite operating at less than full strength is impressive. 

Is Airbnb stock cheap? 

Airbnb stock is trading at a forward price-to-sales ratio of 17.7, so it's certainly not cheap. Its current valuation is below the forward price-to-sales ratio high of 23 it was trading at back in February. Airbnb's excellent prospects are no secret to the markets, which have priced the stock accordingly.

Even so, long-term investors might want to give Airbnb stock a more detailed look right now as it is trading closer to its December 2020 IPO price than it is to the 52-week highs it set in February. Important numbers like advanced bookings revenue suggest the stock could be on its way back up.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.