![](https://developer.android.com/static/images/design/ui/mobile/glossary-hero.png)

Learn Android and UI-related terms.

Activities
:   In Android, an[activity](https://developer.android.com/reference/android/app/Activity)includes an app's UI and the actions it makes available to users. An app is a collection of activities that are created and reused from other apps. Read more on[how activities allow for flexibility in the user journey](https://developer.android.com/guide/components/activities/intro-activities).

CTA
:   Call to action, the primary goal you want your user to achieve. For example,**Subscribe**could be a CTA for letting a user to sign into a service.

Canonical layout
:   Commonly used design compositions that help layouts adapt for common use cases and screen sizes.

Chroma
:   The colorfulness of a color, ranging from neutral gray to full vibrancy.

Containment
:   The concept of visual grouping to create boundaries with use of white space or visible elements.

Density-independent pixels (dp)
:   Flexible units that scale to have uniform dimensions on any screen. They are based on the physical density of the screen. These units are relative to a 160 dpi (dots per inch) screen, on which 1 dp is roughly equal to 1 px.

Display cutout
:   An area on some devices that extends into the display surface to provide space for front-facing sensors.

Hue
:   The perception of color, or how you would describe the color.

Intents
:   An intent allows an app to signal it needs another app's assistance in performing an action; for example, a messaging app can use the Share intent to share a photo from the Photos app with a contact. Apps can indicate which intents to respond to through activities. Android provides flows and UI for a number of intents. Learn about[common intents](https://developer.android.com/guide/components/intents-common).

Navigation bar
:   An Android system bar displayed at the bottom of the screen. It allows the user to navigate a device through either a gesture or tapping a button.

Scalable pixels (sp)
:   Scalable pixels serve the same function as dp, but for fonts. The default value of an sp is the same as the default value for a dp. The Android system calculates the actual font size to use based on the device and the user's preference set in the Settings app of their Android-powered device.

Status bar
:   An Android system bar displayed at the top of the screen. It contains notification icons and system icons.

Tasks
:   A sequence of activities a user follows to accomplish a goal. These activities are arranged in a stack, known as*the back stack* , in the order in which each activity is opened. Learn more about the[back stack lifecycle](https://developer.android.com/guide/components/activities/tasks-and-back-stack).

Tone
:   The luminance, or brightness, of a color. Describes the level of light that a digital color value represents.