![](https://developer.android.google.cn/static/images/design/ui/mobile/glossary-hero.png?authuser=9)
Learn Android and UI-related terms.
- Activities
- In Android, an 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.
- 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.
- 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.
- Tone
- The luminance, or brightness, of a color. Describes the level of light that a digital color value represents.