where the air is unconfined
"he wanted to get outdoors a little"
"the concert was held in the open air"
"camping in the open"
a tournament in which both professionals and amateurs may play
"Many young golfers dream of competing in an open where they can face professional players on the same course."
Open or unobstructed space; an exposed location.
"The hikers chose to camp in a wide-open meadow rather than near the treeline for better visibility."
In plain English: An open is a type of game played with cards where players take turns revealing their hand to others.
"The open on the football field was filled with fans."
Usage: Use "open" as a noun to refer to an open area or exposed location, such as when describing a field with no trees or a wide expanse of water. Avoid using it this way if you simply mean a door or container that is not closed, which should remain a verb or adjective.
begin or set in action, of meetings, speeches, recitals, etc.
"He opened the meeting with a long speech"
spread out or open from a closed or folded state
"open the map"
"spread your arms"
display the contents of a file or start an application as on a computer
"I clicked the icon to open my favorite spreadsheet program so I could finish the report before lunch."
To make something accessible or allow for passage by moving from a shut position.
"She pushed the heavy door open to let everyone into the lobby."
In plain English: To open something means to make it no longer closed so that you can get inside or see what is on the other side.
"She opened the door to let the fresh air in."
Usage: Use "open" to describe the action of moving a door, window, or container so that it can be entered or accessed. This verb applies specifically when an object transitions from a closed state to one where passage is possible.
affording unobstructed entrance and exit; not shut or closed
"an open door"
"they left the door open"
not defended or capable of being defended
"an open city"
"open to attack"
(set theory) of an interval that contains neither of its endpoints
"In the context of real analysis, the notation $(a, b)$ represents an open interval because it includes all points between $a$ and $b$ but excludes the endpoints themselves."
not brought to a conclusion; subject to further thought
"an open question"
"our position on this bill is still undecided"
"our lawsuit is still undetermined"
without undue constriction as from e.g. tenseness or inhibition
"the clarity and resonance of an open tone"
"her natural and open response"
openly straightforward and direct without reserve or secretiveness
"his candid eyes"
"an open and trusting nature"
"a heart-to-heart talk"
Not closed
"The store remained open all night to serve customers who were still shopping after midnight."
able to be accessed
"The manager said the new filing system would not be open until next Monday morning."
In plain English: Open means not closed, allowing things to go in or out freely.
"The open window let in the fresh morning air."
Usage: Use open to describe something that allows entry or access, such as an unlocked door or a welcoming atmosphere. Do not use it to mean physically uncovered when referring to items like jars, which should be described as uncapped or unsealed instead.
The word "open" comes from the Old English term for "open," which traces its roots back to a Proto-Indo-European root meaning "up from under or over." It entered Middle English with this same meaning and has remained unchanged in definition since then.