iBar = this bar, the current bar you're looking at
iFrame = an adjustment value to go from your chart's time frame (ex, 5 minutes) to the Higher Time Frame (ex, 60 minutes), given as (higher time frame in minutes) / (current time frame in minutes)
Ex: current time frame = 5 minutes, higher time frame = 60, so iFrame = 60/5 = 12
meaning, Higher Time Frame indicator changes over 12 bars instead of 1 bar
dValue = MA value at this bar
hfOpen[iBar] = open price of the current bar
hfClose[iBar-iFrame] = close price of bar higher time frame bars ago (see iFrame above)
so this line:
(hfClose[iBar - iFrame] < dValue && dValue < hfOpen[iBar])|| // Positive gap
means "if the close from higher time frame bars ago is less than the MA value, AND the current open is higher than the MA value, THEN do something"
the "// Positive gap" is not part of the code,the author makes a note this case is where the price gaps upwards. But the "||" is an OR, it looks like he has 4 different possible conditions for setting the entry price of the position.
But be sure to test using these indicators on FSB and FST in practice or demo accounts before using them, there have been quite a few posts that the HTF (Higher Time Frame) indicators have some bugs where the FST trade executions don't match the FSB backtesting.
hope that helps