DescribeTab

The describeTabs() call returns a describeTabSetResult object, of which DescribeTab is a property:

Name	Type	Description
colors	DescribeColor[]	Array of color information used for a tab. This field is available in API version 29.0 and later.
custom	boolean	`true` if this is a custom tab, `false` if this is a standard tab.
iconUrl	string	The URL for the main 32 x 32 pixel icon for a tab. This icon appears next to the heading at the top of most pages. This icon URL corresponds to the 32x32 icon used for the current Salesforce theme, introduced in Spring ‘10.
icons	DescribeIcon[]	Array of icon information used for a tab. This field is available in API version 29.0 and later.
label	string	The display label for this tab.
miniIconUrl	string	The URL for the 16 x 16 pixel icon that represents a tab. This icon appears in related lists and other locations. This icon URL corresponds to the 16x16 icon used for the current Salesforce theme, introduced in Spring ‘10.
sobjectName	string	The name of the sObject that is primarily displayed on this tab (for tabs that display a particular SObject). For a list of objects, see Standard Objects.
url	string	A fully qualified URL for viewing this tab.

SOAP API Developer's Guide