There are 3 load reports in the software and these are:

Basically, all 3 reports are very similar in what data they display but for the sake of comprehensiveness let's divide them into 2 categories
Ticket load report
This report contains a table with every hour of the last 30 days. Data only for last 30 days is stored.
MAX Agents  the maximum number of online/logged in agents in the given hour
MIN Agents  the minimum number of online/logged in agents in the given hour
AVG Agents  the values of maximum and minimum numbers are taken every minute in the hour and the AVG agents calculate the average of these numbers. So, for example, 55minutes from the given hour there were 5 agents online and in the remaining 5 minutes, there were only 4 agents online. The average in this scenario would be 4.916 and it would be calculated like this:
(5 agents * 55 minutes + 4 agents * 5 minutes) / 60 minutes
work in progress ticket  a ticket which is opened by an agent, so it is at the main top tab with tickets you have currently opened. Only tickets in status NEW and OPEN are counted as work in progress tickets. So if you are looking at a ticket in status RESOLVED for example it isn't counted as work in progress ticket.
MAX work in progress tickets  the maximum number of work in progress tickets which were opened by agents during any minute in the given hour.
MIN work in progress tickets  the minimum number of work in progress tickets which were opened by agents during any minute in the given hour. If in any single minute during the hour no one had any ticket opened it would show 0 in the column for that hour.
AVG work in progress tickets  the average of these numbers basically the same way as in AVG agents column.
MAX queue  queue in ticket load report means the number of New and Open tickets in the system. So MAX queue shows the maximum number of open/new tickets during any minute within the hour.
MIN queue  MIN queue shows the minimum number of open/new tickets during any minute within the hour.
AVG queue  Works in a similar way as AVG agents, it gets the numbers from every single minute in the given hour and makes an average of them.
Chat and Call load reports
Slots  each agent has a setting which defines how many concurrent chats the agent can take at once, those are slots. If an agent can take up to 4 concurrent chats then he is counted as 4 slots.
MAX slots  the maximum number of available slots in the given hour, so basically the maximal number of chats/calls which could have been taken by your agents on one time during the particular hour. Of course only slots from agents who are available for the given channel are counted here.
MIN slots  the minimum number of available slots in the given hour.
AVG slots  see the AVG Agents calculation above, it works the same way.
MAX chats/calls  the maximum number of chats/calls which were going on during any minute in the given hour.
MIN chats/calls  the minimum number of chats/calls which were going on during any minute in the given hour. If in any single minute during the hour there was no online chat/call happening then this column would show 0 in the particular hour.
AVG chats/calls  the average of these numbers basically the same way as in AVG agents collumn.
MAX queue  the maximum number of customers which were waiting in queue to get on chat/call during any minute within the hour.
MIN queue  the minimum number of customers which were waiting in queue to get on chat/call during any minute within the hour.
AVG queue  Works in a similar way as AVG agents above, it gets the numbers from every single minute in the given hour and makes an average of them.