What is [in] ?

Title says it all, ive tried google and and other search engines but now im going crazy soon

Im trying some programming and get stuck becouse of this:

In the mql4 reference it looks something like this, no need to read closely, its just so you see what im reading...

bool ObjectCreate(
long chart_id, // chart ID
string object_name, // object name
ENUM_OBJECT object_type, // object type
int sub_window, // window index
datetime time1, // time of the first anchor point
double price1, // price of the first anchor point
...
datetime timeN=0, // time of the N-th anchor point
double priceN=0 // price of the N-th anchor point
);

chart_id
[in] Chart identifier.
object_name
[in] Name of the object. The name must be unique within a chart, including its subwindows.
And so on and so on...

What is [in]???????????????????

google returns a crazy amount of in but no [in]

Its used to specify which cart window mark-
https://docs.mql4.com/objects/objectcreate
Its used to specify which chart window you want to plot objects to. Can be either name or index.

The parameter passes an input value ("[in]") only.
There might be parameters that pass an output value ("[out]"), where something will be put (back) (by the callee), i.e. as you can see here: https://msdn.microsoft.com/en-us/lib...(v=vs.85).aspx

Thanx guys, im very new at this, lol