Yellow-back:
‘The nickname given to the particular type of cheap edition evolved in the middle of the 19th century for display and sale on railway bookstalls. It was usually (but not always) a cheap edition of fiction; it usually (but not always) cost two shillings; its basic coloring was usually (but not always) yellow’ (Michael Sadleir)
These books are featured on the British Library website, here.
-from John Carter and Nicolas Barker’s ABC for Book Collectors.
Barker will be here at Wells this Tomorrow, Thursday!