Below is a simulation of the green bar paper which was commonly used in printing terminals like DECwriters and line printers. The bars helped the reader to follow the lines of text on wide printouts and reports. The paper was typically 14 7/8 wide including tractor feed holes on the edges. Normally 132 columns would be printed across the width of the page at 10 characters per inch. The bars were 1/2 inch wide which is 3 lines at 6 lines per inch or 4 lines at 8 lines per inch. If you adjusted the printer carefully your text would neatly fall within the green and white stripes. Otherwise your text would straddle the bar boundaries or the between page perforations.
The holes at the edge are tractor feed holes. The printer mechanism had pins which fit through them to pull the paper through the printer. The paper was about 2500 continuous fan fold pages per box with perforations at 11 inch or 9.5 inch boundaries so the individual pages could be separated after printing. The separation had to be manually performed on all except high end printers which would have been unlikely to be used with a PDP-8. Normally people would leave all the pages for a printout still attached and only separate between the printouts. This had the advantage of keeping pages together and in the right order, no staples needed. It was also convenient for printing arbitrarily long banners.
Other sizes and types of paper were also used such as plain white, blue bar, lined, newsprint quality, multipart forms etc. The teletype used 7.5 inch rolls of paper without any perforations.
Blue bar paper