While “cost per click” is more commonly referring to a “click through rate” for online advertising, the term “click” is also used when print shops generate printing estimates. And it may be the case that you do not see the click charge represented in a print estimate or invoice, however print shops will almost always factor in a click rate cost when determining how much the charge for a print project.
When it comes to digital printing, a click is simply a nominal cost per each sheet that runs through a printer that is being leased by a shop. Due to routine maintenance and repair of the printer, the company who owns the printer will charge a click rate to the print shop in order to cover service cost. Additionally, supplies such as toner may also be included in the lease, which affects the click rate as well. For the most part, printing in color has a higher click rate than printing in grayscale, using just black.
Different print shops will have different click rates, but at the end of the day, the click rate per sheet is typically not very high. That being said, for large print runs, clicks can add up quickly (or clickly?...I'm sorry). To get the most printing for your money, print shops will typically impose your design as many times as possible on a large sheet of paper. By printing more copies per sheet, the click rate is cut down considerably, decreasing cost. For example, if you would like to print 100 copies of an 8.5 x 11 design, it wouldn’t make sense to print one at a time on 8.5 x 11 sheets, when you can impose two copies onto an 11 x 17 (12 x 18 if there is bleed in the artwork). By printing 2-up on a sheet, the total click cost is cut in half.