The columns whose slenderness ratio is less than 80, are known as

* Slenderness Ratio: This is a way to measure how likely a column is to buckle (bend sideways) under a load. It's calculated by dividing the column's effective length by its least radius of gyration.

* Short Columns: These are columns that are relatively stocky. They tend to fail due to crushing (the material being squeezed) rather than buckling.

* Long Columns: These are columns that are relatively slender. They are more likely to buckle under load.

* Medium Columns:These columns behaviour lies between short and long columns.

* General Rule: A common rule of thumb is that columns with a slenderness ratio less than 80 are generally classified as short columns. They primarily fail due to compressive stresses exceeding the material's yield strength.

* Weak Columns: This term isn't directly related to slenderness ratio in the same defining way as short or long columns. A weak column could be weak due to material properties or manufacturing defects, regardless of its slenderness ratio.

Therefore, a slenderness ratio less than 80 indicates a short column that's prone to crushing rather than buckling.