>I have a question about the following design approach for web application which targets are tablet browsers like iPad, Nexus, etc. The approach I choose is the following:
>The main page of the application has a pull-down menu. When user clicks on an item of the menu a new tab is opened. For example, one of the items on the menu is View Order. And I envision that a user may want to see several orders at the same time. So when he/she clicks on this menu anchor, a new tab is opened where user enters order number and views the order. At the same time he/she can click on the same menu item again and open another tab to view another order. And so on. So practically, the main tab/page of the application will host the main menu and some static text (I have not come up with what text though).
>What do you think about this UI approach? Would this type of app be called MPA (Multiple Page Application) as opposed to SPA (Single Page Application)?

Sounds OK to me. It's a MPA.
FWIW, with Chrome on a Nexus when there are multiple tabs they can be scrolled across to find the one you want so it works quite well.

An alternate using SPA might be to put each order as it is loaded into a separate div and arrange things so that only one order was visible at any one time. That way you could implement a 'Close All' behaviour which you couldn't do using separate tabs.....