What does “div” mean in the specifications?

The term “div” for most SIGLENT specifications is equal to the Vertical Scale value (Commonly shown in units of Volts/div).
Take the specification for the DC Gain Accuracy of a SIGLENT SDS1052DL+
For ranges ≤ 100 mV/div, the DC Gain Accuracy is given as
± [3% × (|reading|+|offset|) +1% × |offset| +0.2 * div+2 mV]
If:
Reading = 0.5 V
Offset is 0.1 V
Vertical scale (div) = 100 mV/div = 0.1 V/div,
Then DC Gain is calculated as follows:
± [3% × (|reading|+|offset|) +1% × |offset| +0.2 * div+2 mV] =
± [3% × (|0.5 V|+|0.1 V|) +1% × |0.1 V| +0.2 div * (0.1 V/div) + 0.002 V] =
± [3% × (0.6 V) + 0.0001 V + 0.02 V + 0.002 V] = 0.018 V + 0.0001 V + 0.02 V + 0.002 V = 0.0401 V