Kerb
Kerbs are the raised, usually striped strips at the edge of the track, marking the boundary and deterring drivers from going beyond it.
Also called curb, sausage kerb
Flat kerbs can be driven over freely and are part of the racing line at most chicanes. Aggressive ones — the raised "sausage" type — are designed to unsettle a car badly enough that using them costs more than it gains.
They do not define the track's edge, though. The white line does: a car with all four wheels beyond it has left the track whether or not it touched a kerb.