Difference between 'run:' and 'run: |' in GitHub Actions

What is the difference between run: and run: | in GitHub Actions?

The context can be found here

name: Create Docker Container

on: [push]

jobs:
  mlops-container:
    runs-on: ubuntu-latest
    defaults:
      run:
        working-directory: ./week_7_ecr
    steps:
      - name: Checkout
        uses: actions/checkout@v2
        with:
          ref: ${{ github.ref }}
      - name: Configure AWS Credentials
        uses: aws-actions/configure-aws-credentials@v1
        with:
          aws-access-key-id: ${{ secrets.AWS_ACCESS_KEY_ID }}
          aws-secret-access-key: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
          aws-region: us-west-2
      - name: Build container
        run: |
          docker build --build-arg AWS_ACCOUNT_ID=${{ secrets.AWS_ACCOUNT_ID }} \
                       --build-arg AWS_ACCESS_KEY_ID=${{ secrets.AWS_ACCESS_KEY_ID }} \
                       --build-arg AWS_SECRET_ACCESS_KEY=${{ secrets.AWS_SECRET_ACCESS_KEY }} \
                       --tag mlops-basics .
      - name: Push2ECR
        id: ecr
        uses: jwalton/gh-ecr-push@v1
        with:
          access-key-id: ${{ secrets.AWS_ACCESS_KEY_ID }}
          secret-access-key: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
          region: us-west-2
          image: mlops-basics:latest