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“Monetary policy refers to the actions of central banks to achieve macroeconomic policy objectives such as price stability, full employment, and stable economic growth. Fiscal policy refers to the tax and spending policies of the federal government.”

Board of Governors of the Federal Reserve System

“When policymakers seek to influence the economy, they have two main tools at their disposal—monetary policy and fiscal policy. Central banks indirectly target activity by influencing the money supply through adjustments to interest rates, bank reserve requirements, and the purchase and sale of government securities and foreign exchange. Governments influence the economy by changing the level and types of taxes, the extent and composition of spending, and the degree and form of borrowing.”

International Monetary Fund

“Expansionary fiscal policy—an increase in government spending, a decrease in tax revenue, or a combination of the two—is expected to spur economic activity. When the government’s budget is running a deficit (when spending exceeds revenues), fiscal policy is said to be expansionary."

Congressional Research Service

"Contractionary fiscal policy—a decrease in government spending, an increase in tax revenue, or a combination of the two—is expected to slow economic activity. When it is running a surplus (when revenues exceed spending), fiscal policy is said to be contractionary.”

Congressional Research Service

“Fiscal policy decisions are determined by the Congress and the Administration; the Fed plays no role in determining fiscal policy.”
Board of Governors of the Federal Reserve System

The primary components of mandatory spending are major healthcare programs (Medicare, Medicaid, etc.) and Social Security (OASDI), etc.

Mandatory Spending in Fiscal Year 2020: An Infographic | Congressional Budget Office (cbo.gov)

Some key examples of discretionary spending are defense, transportation, and education.

Discretionary Spending in Fiscal Year 2020: An Infographic | Congressional Budget Office (cbo.gov)

“The government can use contractionary fiscal policy to slow economic activity by decreasing government spending, increasing tax revenue, or a combination of the two. Decreasing government spending tends to slow economic activity as the government purchases fewer goods and services from the private sector. Increasing tax revenue tends to slow economic activity by decreasing individuals’ disposable income, likely causing them to decrease spending on goods and services. As the economy exits a recession and begins to grow at a healthy pace, policymakers may choose to reduce the fiscal stimulus to avoid some of the negative consequences of expansionary fiscal policy, such as rising interest rates, growing trade deficits, and accelerating inflation, or to manage the level of public debt.”
Congressional Research Service

“The government can use fiscal stimulus to spur economic activity by increasing government spending, decreasing tax revenue, or a combination of the two. Increasing government spending tends to encourage economic activity either directly through purchasing additional goods and services from the private sector or indirectly by transferring funds to individuals who may then spend that money. Decreasing tax revenue tends to encourage economic activity indirectly by increasing individuals’ disposable income, which tends to lead to those individuals consuming more goods and services. This sort of expansionary fiscal policy can be beneficial when the economy is in recession, as it lessens the negative impacts of a recession, such as elevated unemployment and stagnant wages. However, expansionary fiscal policy can result in rising interest rates, growing trade deficits, and accelerating inflation, particularly if applied during healthy economic expansions. These side effects from expansionary fiscal policy tend to partly offset its stimulative effects.”
Congressional Research Service

“Counter-cyclical fiscal measures are policy measures which counteract the effects of the economic cycle. For example, counter-cyclical fiscal policy actions when the economy is slowing would include increasing government spending or cutting taxes to help stimulate economic recovery.”
eurostat

Classical examples are taxes and spending. In your macroeconomics classes, these were likely denoted by T and G, respectively. Note that the simple notation is somewhat misleading. There are myriad types of taxes and just as many forms of government spending.

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