Here's a glossary of some common design terms. The quoted definitions come from Wikipedia, and clicking on the word will take you to the Wikipedia page for more info. In some instances I've added notations in brackets for clarification:
CMYK "The CMYK color model (process color, four color) is a subtractive color model, used in color printing, and is also used to describe the printing process itself. CMYK refers to the four inks used in some color printing: cyan, magenta, yellow, and key (black)." [Most color printing is CMYK. —M]
RGB "The RGB color model is an additive color model in which red, green and blue light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three additive primary colors, red, green, and blue." [RGB is used for items that will only be appearing on a screen. —M]
4-Color or Rich Black "Rich black, in printing, is an ink mixture of solid black over one or more of the other CMYK colors, resulting in a darker tone than black ink alone generates in a printing process."
Vector graphics [The preferable graphic type for logos because they can be scaled to any size without losing quality. Common formats include EPS, AI, SVG, and PDF. —M] "Vector graphics use 2D point located polygons to represent images in computer graphics. Each of these points has a definite position on the x- and y-axis of the work plane and determines the direction of the path; further, each path may have properties, including such values as stroke color, shape, curve, thickness, and fill. Vector graphics are commonly found today in the SVG, EPS and PDF graphic file formats and are completely different from the more common raster graphics file formats of JPEG, PNG and MPEG4."
Raster Graphics [Some common raster file formats are JPEG/JPG, GIF, PNG, TIF/TIFF, and PSD. —M] "In computer graphics, a raster graphics or bitmap image is a dot matrix data structure, representing a generally rectangular grid of pixels, or points of color, viewable via a monitor, paper, or other display medium. Raster images are stored in image files with varying formats."
DPI/PPI "Dots per inch (DPI, or dpi) is a measure of spatial printing or video or image scanner dot density, in particular the number of individual dots that can be placed in a line within the span of 1 inch (2.54 cm). Monitors do not have dots, but do have pixels; the closely related concept for monitors and images is pixels per inch or PPI. Many resources, including the Android developer guide, use the terms DPI and PPI interchangeably." [DPI/PPI are used when referring to raster images. Printers usually prefer images to be 300dpi/ppi or more, while screen images can be 72dpi/ppi. —M]
InDesign "Adobe InDesign is a desktop publishing software application produced by Adobe Systems. It can be used to create works such as posters, flyers, brochures, magazines, newspapers, presentations, books and ebooks. InDesign can also publish content suitable for tablet devices in conjunction with Adobe Digital Publishing Suite." [InDesign file names end with .indd or .idml and can only be opened by InDesign. —M]