1 x 4 GB means that it has 1 RAM stick of 4 GB.
To see what the maximum amount of RAM is, either read the manuals or ask on crucial.com.
Is this laptop worth money? HP laptop 15 BW010NM 2KH13EA
And what this means? Can I later upgrade RAM to 16GB?
4 GB DDR4-1866 SDRAM (1 x 4 GB)
And also I am interested in ACER laptop A515 51G 3286, and 4 GB DDR4 SDRAM give me option to upgrade RAM to which level?