a option vs an option

Some examples from the web:

• val may : ('a -> unit) -> 'a option -> unit. may f (Some x) calls f x and may f None does nothing. val map : ('a -> 'b) -> 'a option -> 'b option. map f (Some x) returns ...
• Agilent Technologies, Inc. (A) Option Chain. A. $42.44. *. 0.51. 1.22%. Get A Alerts. *Delayed - data as of Apr. 7, 2015 - Find a broker to begin trading A now.
• In the OCaml language, the option type is defined as type 'a option = None | Some of 'a . In the Scala language, the option type is defined as parameterized ...
• Some : A -> option A | None : option A. Definition option_map (A B:Type) (f:A->B) o := match o with | Some a => Some (f a) | None => None end. sum A B, written ...

Some examples from the web:

• An option is a contract to buy or sell a specific financial product known as the option's underlying instrument or underlying interest. For equity options, the ...
• The expression "writing an option" refers to the act of selling an option. An option is the right, but not the obligation, to buy or sell a particular trading instrument at ...
• An option is a contract that gives the buyer the right, but not the obligation, to buy or sell an underlying asset at a specific price on or before a certain date.
• For example, because the option writer will need to provide the underlying shares in the event that the stock's market price will exceed the strike, an option writer ...