What is --from used in copy command in dockerfile

Question

I am including the dockerfile code:

FROM mcr.microsoft.com/dotnet/aspnet:5.0-buster-slim AS base
WORKDIR /app
EXPOSE 80
EXPOSE 443

FROM mcr.microsoft.com/dotnet/sdk:5.0-buster-slim AS build
WORKDIR /src
COPY ["FirstDockerApp/FirstDockerApp.csproj", "FirstDockerApp/"]
RUN dotnet restore "FirstDockerApp/FirstDockerApp.csproj"
COPY . .
WORKDIR "/src/FirstDockerApp"
RUN dotnet build "FirstDockerApp.csproj" -c Release -o /app/build

FROM build AS publish
RUN dotnet publish "FirstDockerApp.csproj" -c Release -o /app/publish

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "FirstDockerApp.dll"]

I'm not sure why the 2rd last line from below,(COPY --from=publish /app/publish) why is it used or what it accomplishes. Could you perhaps assist me in comprehending it?