Use the @default, @defaultVal or @defaultValue flags:
@default Something
@defaultVal "foo"
@defaultValue 42
In a property
@property foo
@type object
@default "bar"
Include the default value by attaching it to the name with an equal sign.
In a method param tag:
@param {type} arg1=foo - description
In a "quick prop" property:
@property {object} foo="bar" - description
The equal sign must butt-up against the name and the value:
arg1=foo
arg1 = foo