Theme - basically, a theme is a way to dress up your website. On the other hand, it is more that just “clothes”. Dressing up a site means that only design is changed, but a theme provides much more control over the look and presentation of the information on your website. A WordPress theme is made of template files that work together to produce a graphical interface with an underlying unifying design for a website. The key issue in the notion of the theme is that it modifies the look of your site without changing the software.
Child theme - a theme that works off another (parent) theme. Sometimes these can be referred to as skins but more accurately are a separate theme you install which requires the other ‘parent’ to work.
Theme options (settings) - a special options panel to configure elements of the site without implementing any coding.
Column - a way to organize content on a page. A two column theme means one content column and one sidebar. If you want two sidebars, you will need a three column theme.
Widget ready - a theme that has areas where you can place widgets.
Fixed width - the width of the theme does not change according to screen resolution (or the width of browser) your visitors use.
Fluid width - the width of the theme changes according to screen resolution (or the width of browser) your visitors use.
Responsive width means the the layout adapts depending on the size of the device being used to view your site. When responsive width themes are viewed on mobiles, sidebars appear below the posts in order to provide as much space as possible for reading.
Translation-ready - a theme supports multi-language option, but translation should be added manually.