Replace 'ISO image'

wiki/src/install/expert/usb.mdwn

@@ -160,7 +160,7 @@ Install Tails using <span class="command">dd</span>
    <strong>you risk overwriting any hard disk on the system</strong>.</p>
    </div>
 
-1. Execute the following commands to copy the ISO image that you
+1. Execute the following commands to copy the USB image that you
    downloaded earlier to the USB stick.
 
    Replace:

wiki/src/install/inc/steps/restart_first_time.inline.mdwn

@@ -220,7 +220,7 @@ the rest of the instructions afterwards, we recommend you either:
 
    1. Which version of Tails are you trying to start?
 
-   1. How did you verify the ISO image?
+   1. How did you verify the USB image?
 
    1. Which is the brand and model of the computer?
 

wiki/src/upgrade/tails.mdwn

@@ -15,7 +15,7 @@
 Install an intermediary Tails
 =============================
 
-In this step, you will install an intermediary Tails using the Tails ISO
+In this step, you will install an intermediary Tails using the Tails USB
 image that you downloaded earlier.
 
 <div class="note">