This is an advanced-use feature, and likely not something you'll need to configure. What you probably want is the content types reference

The textarea field represents a multi-line text input. It should be used for content values that are long strings: for example, a page description.

tinacms-textarea-field

Options

interface TextareaConfig {
  name: string
  component: 'textarea'
  label?: string
  description?: string
}
OptionDescription
componentThe name of the plugin component. Always 'textarea'.
nameThe path to some value in the data being edited.
labelA human readable label for the field. Defaults to the name. (Optional)
descriptionDescription that expands on the purpose of the field or prompts a specific action. (Optional)

This interfaces only shows the keys unique to the textarea field.

Visit the Field Config docs for a complete list of options.

Example: A Blog Post Description

Below is an example of how a textarea field could be used to edit the description of a blog post.

const BlogPostForm = {
  fields: [
    {
      name: 'description',
      component: 'textarea',
      label: 'Description',
      description: 'Enter the post description here',
    },
  ],
}