Most airlines offer some type of flight privileges. They're generally referred to as NRSA - non-revenue space available. Under US tax law, they can be offered free to employees, spouses, dependents (26 or under), and parents. I think all US airlines now let you designate a "travel companion" or domestic partner in lieu of a spouse. Often, there is a small charge for the passes. Because of tax rules, the cost to the employee for a travel companion/domestic partner is greater. The cost for the travel companion is either imputed income (a tax concept) or more commonly now a mileage based charge that is supposed to relate to the fair market value of the standby ticket. Most domestic airlines offer buddy passes. I worked for both Delta and American; they both offer 8 buddy passes per year. Employees are charged a mileage based charge like that described above.

Additionally, employees are able to purchase "positive space" tickets from their own airline at a 20% discount. There are also "interline" benefits on other airlines, cargo airlines (e.g., FedEx), cruises, hotels, etc.

The air travel privileges are space available and there is a priority for boarding. AA used when you checked in (but not more than 4 hrs in advance). DL used seniority. Employees and families are ahead of buddies. Most airlines offer one or more passes a year at a higher priority and most also give priority to thru passengers.

The passes let you go anywhere so long as no one wants to go there. Buddy passes often get embargoed because the loads are so high, there's no chance they'll get on.

I once went to Buenos Aires for lunch on passes. Got Business class both ways. They can be a lot of fun but they can also leave you sitting at the airport for a couple of days waiting to get on a flight.

Finally, the passes can and do differ for employees in other countries and for airlines based in other countries. Often the differences are related to tax laws. Sometimes they are related to culture and employee expectations.