According to Flu.gov:
A pandemic is a global disease outbreak. It is determined by how the disease spreads, not how many deaths it causes.
When a new influenza A virus emerges, a flu pandemic can occur. Because the virus is new, the human population has little to no immunity against it. The virus spreads quickly from person-to-person worldwide.
The United States is not currently experiencing a flu pandemic. If a pandemic occurs, the federal government will work to identify the cause and create a vaccine. Flu.gov will provide updates on the steps the federal government is taking to address the pandemic.