All predefined timeframes of charts have unique identifiers. The PERIOD_CURRENT identifier means the current period of a chart, at which a mql4-program is running.
The ENUM_TIMEFRAMES enumeration contains the values of standard timeframes, online charts of financial instruments can be plotted only on these time intervals.
Below are non-standard timeframes, in MQL4 they are constants.
These periods can be used for working with offline charts.
The constants of non-standard timeframes are included in the MQL4 language to enable translation and compilation of MQL5 programs, where these timeframes are standard and are included in the ENUM_TIMEFRAMES enumeration.