The first character in the file name refers to whether it is a balanced or unbalanced instance.
The second character is the number of rows of the instance. (i.e. the height)
The third character is the number of columns of the instance. 
The fourth and fifth characters refer to the density of containers. (i.e. if it is 55, that means 55% of the system is full)
The last two charcters refer to the instance number with the same parameters. (starts with 10 and ends with 49. So we have 40 random instances with the same parameter)