For most of us, flying is still an inherently mysterious activity.

To shed some light on the world of commercial air travel, Business Insider turned to Patrick Smith for some answers. Smith is not only an author and aviation blogger, but he is also a long-time commercial airline pilot flying Boeing 757 and Boeing 767 jets.

Smith, who wrote “Cockpit Confidential,” compiled a glossary of commonly misunderstood airline jargon on his website, AskThePilot.

According to Smith, some of the terms are highly technological while others are quite humorous and even a bit absurd.

Here’s a selection of entries:

– “Doors to arrival and crosscheck”

Used in a sample sentence: “Flight attendants, doors to arrival and crosscheck.”

Definition: The announcement, usually made by the lead flight attendant as the plane is approaching the gate, is to verify that the emergency escape slides attached to each door have been disarmed — otherwise the slide will deploy automatically as soon as the door is opened.

– “All-call”

Used in a sample sentence: “Flight attendants, doors to arrival, crosscheck and all-call.”

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Definition: According to Smith, all-call is usually part of the door arming/disarming procedure. “This is a request that each flight attendant report via intercom from his or her station — a sort of flight attendant conference call,” he wrote.

– “Holding pattern”

Definition: “A racetrack-shaped course flown during weather or traffic delays,” Smith wrote. “Published holding patterns are depicted on aeronautical charts, but one can be improvised almost anywhere.”

Read more: Business Insider