Variables
barstate.islast
The bar your script is on is the last bar of the chart. On every bar before it, this reads false. It marks a single position in the series rather than a range of bars.
Example
indicator("BarState.islast Example", overlay=true)
plotshape(barstate.islast, location=location.abovebar, shape=shape.triangleup, color=color.red, size=size.small)
Type
series bool