Batteries are classed, categorised and rated to international standards. Those standards can also be manipulated when published if you state your variances, the trick is to know what's important and why.
In the Aviation industry battery is rated at the 1 hour rate because if your batteries fail while in flight you better hope you can get on the ground within 30 minutes before you lose communication or navigation instrumentation. This means a battery rated a 10Ah @ the 1-hour rate can provide 10A until it's voltage reaches 10.02 volts or 1.67 volt per cell and is considered completely flat. (sometimes the end voltages are much lower to make a batteries capacity seem better).
Traction batteries like used in Electric Forklifts are rated at a 5 or 8-hour rate because depending on the type of products being picked the equipment might average 5 used hours in one shift. Other products might require more handling in an 8-hour shift so you would use the 8 hour rate. Either way the end result would be flat batteries by the end of shift, which once recharged is 1 cycle. If you use larger batteries you can lift the depth of discharge from say 50% to 60% and that will manipulate the depth of discharge (end voltage when flat) and the increased cycle life from say 2000 cycles to 2500 cycles will extend the replacement time (in years) and your Return On Investment (R.O.I).
Industrial Applications use power over a working day with lunch breaks so a 10 hour rate is used. i.e. 18Ah battery at the 10 hour rate will provide 1.8A of power for 10 hours until the voltage is reduced to 10.02 volts. (If the temperature is higher or lower it will change the batteries rated capacity).
General use, deep cycle & Automotive/Marine batteries use the 20 hour rate or Amps over 20 hours so again you divide the stated Ah by 20 hours to get the average current discharge per hour. 100Ah / 20 hours = 5 Amps per hour. (All to often we see all the ampere ratings, temps, end voltages, and battery purposes cross over to confuse and or mislead a buyer as to how good a battery will perform not to mention the variations in a batteries weight).
Solar use the 24 hour rate for daily averages, but the 100 hour rate or 120 hour rate are more common as they refer to a better average use over 4 or 5 days.
You can see how when batteries are advertised at a rate that differs from these industry standards that the designed purpose of the battery may have been for a different use and that it may mean the charging rates need to be different, the voltages might need to be different or that the cycle life could be more or less than your expected use with consequences good or bad.