I am translating a piece of text and there's a short mention about ship's sails. I don't know what kind of ship it is but the author speaks about double-reefed mainsail, foresail and second-sized jib. What is the difference between foresail and jib? What does it mean "second-sized". Does it perhaps mean that there are other kinds of jibs as well and this one is smaller in size?

Thank you for your answer.
Ship's rigging and terminology does vary considerably with the type of ship, but basically the foresail is tied to the foremast at top and bottom, while the jib is tied to the bowsprit at the bottom (and please realize that I am using laymen's terms!) And jibs do come in various sizes, to be used under various wind conditions. I don't think the sizes are standardized, however.
The type of vessel is most probably a schooner. The schooner rig comprises, from the stern forward, a mainsail (the largest sail), a foresail (smaller) and a variety of jibs at the bow.
There are 2 masts, the mainmast and the foremast plus (typically) a bowsprit. As previously noted the jibs are set between the foremast and the bowsprit; they are triangular.
The main and fore are attached to their respective vertical masts along the forward edge and are approximately rectangular with horizontal spars (boom below and gaff above) at the top and bottom.
To reef a sail means to reduce its area and is done when the wind speed increases to insure that the vessel remains controllable. Reefing is accomplished by gathering a band of sail cloth just above the boom and lashing it securely to the boom with lines sewn through the sail in a horizontal row. Normally 2 or more rows of these "reef points" are provided allowing progressive reductions of sail area. Double reefed means that 2 bands of cloth have been secured and indicates a strong breeze.
The meaning of "second-sized" is a little vague but one can infer from the double reefed main and fore that this would be a smaller jib then the normally set #1.
A picture is worth-----. Look up schooner rig and you will see what I mean.
Hope this helps.