Konsole is the KDE terminal application. It can be configured in many ways, supports transparency (for desktop only), background images, encoding, pre-defined colour schemes (you can make custom ones), tabs (so you can have several sessions opened without the need to open another Konsole), and it's very rich regarding the configuration options.

Gnome Terminal
This is GNOME's default terminal, and features desktop transparency and background images, encoding, profiles and more via the Edit -> Current Profile... configuration dialogue.

Yakuake
Yakuake is yet another terminal emulator for KDE. When I first started it, a notification balloon appears saying to press F12 in order to start it.

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