CUBIC is a network congestion avoidance algorithm for TCP which can achieve high bandwidth connections over networks more quickly and reliably in the face of high latency than earlier algorithms.
[9] CUBIC is a less aggressive and more systematic derivative of BIC TCP, in which the window size is a cubic function of time since the last congestion event, with the inflection point set to the window size prior to the event.
Next is the convex growth where CUBIC probes for more bandwidth, slowly at first then very rapidly.
[10] Another major difference between CUBIC and many earlier TCP algorithms is that it does not rely on the cadence of RTTs to increase the window size.
With earlier algorithms like TCP New Reno, flows with very short round-trip delay times (RTTs) will receive ACKs faster and therefore have their congestion windows grow faster than other flows with longer RTTs.
CUBIC allows for more fairness between flows since the window growth is independent of RTT.
Apart from window based algorithms like Cubic, there are rate based algorithms (including TCP BBR from Google) that works differently using "sending rate" instead of the window.